1. Field
The following description relates to an optical pickup and an optical drive adopting the optical pickup.
2. Description of the Related Art
A 3-beam type optical pickup may obtain a single main beam and two sub beams by using a diffraction element disposed between a beam splitter and a light source. A light receiving sensor that converts light reflected from a medium into an electrical signal may include a main beam region that the main beam reaches and two sub beam regions that the sub beams reach and that are disposed at opposite sides of the main beam region.
A photodetector of an optical pickup used for compact discs (CDs), Blu-ray Discs (BDs), and digital versatile discs (DVDs) may include a light receiving sensor for CDs and a light receiving sensor for BDs/DVDs, which are generally integrated in a single substrate. In addition, a light source for emitting a short wavelength light for BDs and a twin light source for CDs/DVDs may be separately disposed as light sources. The twin light source has a structure in which an emission chip for CDs and an emission chip for DVDs are integrated on a single base (wafer or substrate). The base is disposed to lean with respect to the plane of a medium or the body of the optical pickup. The base leans in such a way that the light receiving sensor for CDs and the light receiving sensor for BDs/DVDs do not overlap with each other. If the gradient of the base decreases, both of the light receiving sensors may be moved closer to each other. On the other hand, if the gradient of the base increases, both of the light receiving sensors may be moved away from each other. However, the gradient of the base may not be increased in an ultra-thin optical pickup having a thickness of 4 mm or less. If the gradient of the base is less than a predetermined level, both of the light receiving sensors overlap each other, which may prevent design of light receiving sensors corresponding to each medium.
FIG. 1 illustrates a schematic structure of an example of a conventional optical pickup compatibly used with a plurality of mediums such as CDs, BDs, and DVDs.
The optical pickup shown in FIG. 1 includes a light transport system (or transmission system) 10 that directly corresponds to a medium 1, a light emitting system 20 that supplies light for reproducing information from and/or writing information onto the medium 1, and a light receiving system 30 that receives light reflected from the medium 1 and generates an electrical reproduction signal to reproduce information.
The light transport system 10 includes an objective lens assembly 11 that corresponds to the medium 1, a first beam splitter 13 having a plate-shape structure, and a collimating lens 12 disposed between the objective lens assembly 11 and the first beam splitter 13. The objective lens assembly 11 includes first and second objective lenses 11a and 11b corresponding to a plurality of mediums. The first objective lens 11a corresponds to CDs and DVDs, and the second objective lens 11b corresponds to BDs. The first and second objective lenses 11a and 11b are aligned to be parallel to the medium 1 and share an optical axis that is perpendicular to both the medium 1 and an optical axis x1 of the transmission system 10. An optical path including the optical axis x1 and the optical axis of the objective lens assembly 11 is refracted by an optical path changing mirror 14. That is, the optical path changing mirror 14 is disposed between the collimating lens 12 disposed on the optical axis x1 parallel to the medium 1 and the first and second objective lenses 11a and 11b disposed on the optical axis perpendicular to the medium 1. The objective lens assembly 11 makes a reciprocating motion so that the first objective lens 11a or the second objective lens 11b can be disposed on the optical axis of the transmission system 10 according to the type of the medium.
The first beam splitter 13 reflects light emitted from the light emitting system 20 in a direction that allows the light to be incident on the medium 1 and light reflected from the medium 1 is transmitted through the first beam splitter 13 and is incident on the light receiving system 30.
The light receiving system 30 includes a photodetector 32 on which the light reflected from the medium 1 is incident and a sensing lens 31 condenses the light on the photodetector 32 to an appropriate size.
The light emitting system 20 includes a plurality of light sources corresponding to the medium 1, for example, a first light source 21a for CDs/DVDs and a second light source 21b for BDs. The first and second light sources 21a and 21b irradiate light toward first and second incidence surfaces 24a and 24b, respectively, of a cubical second beam splitter 24. A coupling lens 23 is disposed between the second light source 21b and the second beam splitter 24 to control an optical magnification, i.e., a defocused amount of a proceeding light. The second beam splitter 24, which receives the light from the second light source 21b, has the two incidence surfaces 24a and 24b, which are adjacent, and adjacent second and first emission surfaces 24c and 24d. Most of light that is incident on the two incidence surfaces 24a and 24b from the first and second light sources 21a and 21b proceeds toward the first beam splitter 13 via the first emission surface 24d. A first diffraction element (grating) 22a for CDs/DVDs and a second diffraction element (grating) 22b for BDs each generate a main beam and sub beams (first diffraction light), and are respectively disposed between the cubical second beam splitter 24 and each of the first and second light sources 21a and 21b. As well-known in the art, intervals between a main beam and a sub beam vary according to grating intervals of the first and second diffraction elements 22a and 22b. Meanwhile, a monitor photodetector 25 is disposed in front of the second emission surface 24c of the second beam splitter 24 to detect light emitted from the second beam splitter 24. The monitor photodetector 25 may be disposed at a side of the first beam splitter 13.
Meanwhile, the coupling lens 23 is disposed between the second light source 21b and the second incidence surface 24b to adjust an optical distance between the second light source 21b and the medium 1 so that light from the second light source 21b may be incident on the collimating lens 12 at an appropriate angle.